Apparatuses and methods for calibrating sense amplifiers in a semiconductor memory

ABSTRACT

Apparatuses and methods for calibrating sense at in a semiconductor memory are disclosed. An example apparatus includes an amplifier circuit and a calibration circuit. The amplifier circuit is configured to be coupled to a supply voltage and a reference voltage, and when activated the amplifier circuit is configured to provide an output signal at an output that is complementary to an input signal provided to an input. When activated by a calibration signal, the calibration circuit is configured to provide a calibration voltage to the of the amplifier circuit, wherein the calibration voltage is in equilibration voltage between the supply voltage and the reference voltage provided to the amplifier circuit.

BACKGROUND

High data reliability, high speed of memory access lower powerconsumption and reduced scaling of chip size are features that aredemanded from semiconductor memory. The reduced scaling of the chip sizetypically results in smaller feature sizes the various circuits ofsemiconductor memory. For example, in a memory array included in asemiconductor memory, memory cells, access line, sense line, senseamplifiers, as well as other circuits in the memory array are designedwith smaller feature sizes. The circuits with smaller feature sizes maybe more susceptible to process variations which cause variations incircuit performance from ideal circuit characteristics. Lower powerconsumption is often achieved by using lower internal voltages, such asusing lower voltages for driving internal signals, for storing in thememory cells, etc. A consequence of the reduced scaling and reduction inpower consumption is that the internal signals become challenging todetect and to transmit on signal lines.

With regards to memory cells and reading information stored in thememory cells, in particular in volatile memory, such as dynamic randomaccess memory (DRAM), the continuous scaling of semiconductor memory andreduction in power consumption has a direct impact on the design andperformance of the sense amplifiers that are used to read out theinformation stored in the memory cells. For example, the reduction ofthe memory cell dimensions and the increase of interconnection parasiticcapacitance and resistance may result in difficulties in accuratelyreading stored information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a portion of a semiconductor memoryincluding a sense amplifier according to an embodiment of thedisclosure.

FIG. 2 is a schematic diagram of a sense amplifier according to anembodiment of the disclosure.

FIG. 3A is a timing diagram showing various signals during operation ofthe sense amplifier of FIG. 2 according to an embodiment of thedisclosure. FIG. 3B is a timing diagram showing various signals duringoperation of the sense amplifier according to an embodiment of thedisclosure.

FIG. 4 is a schematic diagram of a sense amplifier according to anembodiment of the disclosure.

FIG. 5 is a timing diagram showing various signals during operation ofthe sense amplifier of FIG. 4 according to an embodiments of thedisclosure.

FIG. 6 is a schematic diagram of a sense amplifier according to anembodiment of the disclosure.

FIG. 7 is a timing diagram showing various signals during operation ofthe sense amplifier of FIG. 6 according to an embodiment of thedisclosure.

FIG. 8 is a schematic diagram of a pass gate circuit according to anembodiment of the disclosure.

FIG. 9A is a schematic diagram of an inverter circuit according to anembodiment of the disclosure. FIG. 9B is a schematic diagram of aninverter circuit according to an embodiment of the disclosure.

FIG. 10 is a block diagram of a memory including a sense amplifieraccording to an embodiment of the disclosure.

DETAILED DESCRIPTION

Certain details are set forth below to provide a sufficientunderstanding of embodiments of the disclosure. However, it will beclear to one skilled in the art that embodiments of the disclosure maybe practiced without these particular details. Moreover, the particularembodiments of the present disclosure described herein are provided byway of example and should not be used to limit the scope of thedisclosure to these particular embodiments. In other instances,well-known circuits, control signals, timing protocols, and softwareoperations have not been shown in detail in order to avoid unnecessarilyobscuring the disclosure.

FIG. 1 is a block diagram of a portion of a semiconductor memory inaccordance with an embodiment of the present disclosure. As shown inFIG. 1, the portion shown includes a memory array 110. The memory array110 includes a plurality of access lines WL, a plurality of sense linesDL, and a plurality of memory cells MC arranged at intersections of theplurality of access lines WL and the plurality of sense lines DL. Thememory cells MC included in the memory array 110 may be, for example,volatile memory cells (e.g., DRAM memory cells, SRAM memory cells,etc.), non-volatile memory cells (e.g., flash memory cells, PCM cells,etc.), some other types of memory cells, or combinations of variousmemory cells. The memory array 110 may be configured as a plurality ofmemory banks in some embodiments of the disclosure. In accessing thememory cells MC of the memory array 110, a row decoder 112 selects theaccess line WL and a column decoder 114 selects the sense line DLaccording to row addresses and column addresses corresponding to thememory cells to be accessed. A plurality of sense amplifiers SAMP 118are coupled to corresponding sense lines DL to sense and amplifyvoltages representing data stored by the memory cells MC. The senseamplifiers SAMP 118 are coupled to local I/O line pairs LIOT/B. Thelocal IO line pairs LIOT/B are coupled to main IO line pairs MIOT/B viatransfer gates TG which function as switches. The main IO line pairsMIOT/B are coupled to the read/write circuit 120, which is coupled toinput and output circuits (not shown) that receive and provide data forthe semiconductor memory.

FIG. 2 is a schematic diagram of a sense amplifier 200 according to anembodiment of the disclosure. The sense amplifier 200 may be used as asense amplifier 118 in the apparatus 110 of FIG. 1 in sonic embodimentsof the disclosure. The sense amplifier 200 may be coupled to a senseline DL that is used to provide a voltage corresponding to data storedby a memory cell MC. The memory cell MC may be accessed by activating anaccess line WL to cause a voltage stored by the memory cell MC to beprovided to the sense line DL. The voltage stored by the memory cell MCcorresponds to data, for example, a first voltage corresponds to a “1”bit of data and a second voltage corresponds to a “0” bit of data. Thechange in voltage caused by coupling the memory cell MC to the senseline DL is sensed and amplified by a sense amplifier, for example, thesense amplifier 200.

In some embodiments of the disclosure, for example, as shown in FIG. 2,the memory cell MC may be a volatile memory cell that includes a memorycell switch SW and a memory cell capacitor CCELL. However, the scope ofthe disclosure is not intended to be limited to any particular type ofmemory cell and in other embodiments of the disclosure the memory cellMC may be different that that shown in FIG. 2. For example, othervolatile memory cells, as well as non-volatile memory cells, may be usedin embodiments of the disclosure. Example memory cells include, but arenot limited to, memory cells including multiple transistors and/ormultiple capacitors (e.g., 2T-1C memory cells, 2T-2C memory cells, 3T-2Cmemory cells, etc.), floating gate memory cells, magnetic memory cells,phase change memory cells, ferroelectric memory cells, etc.

In embodiments of the disclosure including a memory cell where the datastored by the memory cell is destroyed when the memory cell is accessed(i.e., destructive read), upon completion of the sensing andamplification of the voltage provided by an activated memory cell MC,data should be “written back” to the memory cell MC before deactivatingthe memory cell. Data may be written back to the memory cell MC byapplying a voltage to the sense line DL that corresponds to the dataoriginally stored by the memory cell MC.

The sense amplifier 200 includes an amplifier circuit 210 and acapacitor 215 through which an input of the amplifier 210 is coupled tothe sense line DL. The capacitor 215 may be implemented by any circuitknown to those of ordinary skill in the art. The amplifier circuit 210is configured to be coupled to a supply voltage (e.g., provided by apower supply VCC) and a reference voltage (e.g., reference voltage VSS).The amplifier circuit 210 receives an input signal IN having a voltagerepresenting input data provided by the sense line DL and provides anoutput signal OUT having a voltage representing output data. In someembodiments of the disclosure, the amplifier circuit 210 may beimplemented as an inverter circuit, for example, as shown in FIG. 2. Asa result, the amplifier circuit 210 provides an output signalrepresenting output data complementary to the input data. The amplifiercircuit 210 may include other circuits in other embodiments of thedisclosure.

The sense amplifier 200 further includes a calibration circuit 225. Thecalibration circuit 225 couples an output of the amplifier circuit 210to its input when activated by an active calibration signal CALIB. Thecalibration circuit 225 may include a pass gate circuit in someembodiments of the disclosure, for example, as shown in FIG. 2. Aninverter circuit 220 and pass gate circuit 230 included in the senseamplifier 200 are coupled to the input, output, and the sense line DL asa data latch circuit. The inverter circuit 220 is activated by an activelatch signal SAL and the pass gate circuit 230 is activated by an activelatch signal SAL2. The inverter circuit 220 provides an output signalhaving a logic level complementary to the output signal OUT of theamplifier circuit 210 when activated by the SAL signal, and the passgate circuit 230 couples the input of the amplifier circuit 210 to thesense line DL when activated by the SAL2 signal.

A precharge circuit 240 precharges the sense line DL when activated bythe precharge activation signal WRITE by setting a voltage of the senseline DL to a precharge voltage WRITEVAL in preparation for a senseoperation by the sense amplifier 200. The precharge circuit 240 may beimplemented as a pass gate circuit in some embodiments of thedisclosure, for example, as shown in FIG. 2. In some embodiments, theprecharge voltage is 0.6 volts, which may be one-half the supplyvoltage.

Operation of the sense amplifier 200 will be described with reference toFIG. 2, and FIGS. 3A and 3B. FIG. 3A is a timing diagram showing varioussignals during operation of the sense amplifier 200 for a memory cellstoring low logic level data according to an embodiment of thedisclosure. FIG. 3B is a timing diagram showing various signals duringoperation of the sense amplifier 200 for a memory cell storing highlogic level data according to an embodiment of the disclosure.

With reference to FIG. 3A, prior to time T0, the memory cell MC isdeactivated by inactive access line WL, and the sense line DL isprecharged to a precharge voltage. The sense line DL is prechargedthrough the precharge circuit 240 which is activated by the active WRITEsignal to provide the WRITEVAL voltage to the sense line DL. Theprecharge voltage WRITEVAL is shown in FIG. 3A to be 0.6 volts in theembodiment of FIG. 3A. The precharge voltage may be other voltages inother embodiments of the disclosure, however. Also prior to time T0, thecalibration circuit 225, the inverter circuit 220, and the pass gatecircuit 230 are deactivated, respectively, by inactive CALIB, SAL, andSAL2 signals. The voltage of the precharged sense line DL results in theamplifier circuit 210 being provided a IN signal that causes theamplifier circuit 210 to provide an OUT signal corresponding to a lowlogic level.

At time T0, the calibration circuit 225 is activated by an active CALIBsignal to couple together the input and output of the amplifier circuit210. The coupling of the input and output of the amplifier circuit 210causes voltages of the input and output to equalize to an equilibrationvoltage between the voltages of the high and low logic levels, as shownin FIG. 3A by the IN and OUT signals. In some embodiments of thedisclosure, the equilibration voltage is one-half of the supply voltage.However, it will be appreciated that the scope of the disclosure is notintended to be limited to an equilibration voltage of specificallyone-half of the supply voltage. The coupling of the input and output ofthe amplifier circuit 210 together causes the output to be at a voltagecorresponding to an equilibrium point for the amplifier circuit 210. Theequilibrium point may be the condition corresponding to the maximum gainof the amplifier circuit 210. Providing the equilibration voltage to theinput and the output may compensate for variations of the amplifiercircuit 210 from ideal amplifier characteristics. For example, deviationfrom ideal amplifier characteristics due to circuit mismatch, thresholdvoltage variations, voltage offsets, etc. may be corrected by forcingthe output of the amplifier circuit 210 to the equilibration voltage.

At time T1, the precharge circuit 240 is deactivated by the inactiveWRITE signal to decouple the sense line DL from the WRITEVAL voltage.Following time T1, the calibration circuit 225 is deactivated bydeactivation of the CALIB signal to decouple the input and output of theamplifier circuit 210. Following deactivation of the calibration circuit225, the access line WL is activated to activate the memory cell MC foraccess. The access line WL is shown in FIG. 3A as increasing to avoltage of 2.2 volts for activation. However, other voltages may be usedfor an activated access line WL in other embodiments of the disclosure.Upon activation of the memory cell MC at time T2, the voltage of thesense line DL is changed by the voltage corresponding to the data storedby the memory cell MC. In FIG. 3A, the memory cell MC accessed at timeT2 stores a “0” logic level, corresponding to a voltage less than theprecharge voltage WRITEVAL. As a result, the activated memory cell MCcauses the voltage of the sense line DL to decrease, as shown in FIG. 3Aat time T2.

The decrease in the voltage of the sense line DL due to the activatedmemory cell MC is coupled through the capacitor 215 to cause the voltageof the IN signal for the amplifier circuit 210 to decrease. The decreasein the voltage of the IN signal causes the amplifier circuit 210 toprovide an OUT signal having a voltage corresponding to a high logiclevel, which is complementary to the low logic level corresponding tothe voltage decrease of the sense line DL.

At time T3, the inverter circuit 220 is activated by an active SALsignal to provide a voltage to the sense line DL corresponding to thelow logic level, that is, the complement to the high logic level of theOUT signal provided by the amplifier circuit 210. The low logic levelvoltage provided by the inverter circuit 220 to the sense line DL iscoupled through the capacitor 215 to cause the voltage of the IN signalto further decrease, as shown between times T3 and T4. At time T4, thepass gate circuit 230 is activated by an active SAL2 signal to providethe voltage of the sense line DL to the input of the amplifier circuit210, as shown by the IN signal. Thus, in addition to the voltage of thesense line DL being coupled to the input of the amplifier circuit 210through the capacitor 215, the voltage of the sense DL is coupledthrough the activated pass gate circuit 230 at time T4. With theinverter circuit 220 and the pass gate circuit 230 activated at times T3and T4, the logic level of the OUT signal is latched and the voltage ofthe sense line DL corresponds to the data that was stored by the memorycell MC. Thus, the voltage of the sense DL may be used to write backdata to the activated memory cell MC for those embodiments of thedisclosure where write back is necessary.

With reference to FIG. 3B, the operation of the sense amplifier 200 issimilar to that previously described with reference to FIG. 3A. However,as previously described, FIG. 3B is a timing diagram showing varioussignals during operation of the sense amplifier 200 for a memory cellstoring high logic level data according to some embodiments of thedisclosure.

The operation of the sense amplifier 200 in FIG. 3B is similar to thatas described with reference to FIG. 3A through to about time T2.However, in FIG. 3B, upon activation of the memory cell MC at time T2,the voltage of the sense line DL is increased to greater than theprecharge voltage WRITEVAL because of the high logic level voltagecorresponding to the “1” logic level stored by the memory cell MC. As aresult, the activated memory cell MC causes the voltage of the senseline DL to increase, as shown in FIG. 3A at time T2. The increase in thevoltage of the sense line DL due to the activated memory cell MC iscoupled through the capacitor 215 to cause the voltage of the IN signalprovided to the amplifier circuit 210 to increase. The increase in thevoltage of the IN signal causes the amplifier circuit 210 to provide anOUT signal having a voltage corresponding to a low logic level, which iscomplementary to the high logic level corresponding to the voltageincrease of the sense line DL.

At time T3, the inverter circuit 220 is activated by an active SALsignal to provide a voltage to the sense line DL corresponding to thehigh logic level, that is, the complement to the low logic level of theOUT signal provided by the amplifier circuit 210. The high logic levelvoltage provided by the inverter circuit 220 to the sense line DL iscoupled through the capacitor 215 to cause the voltage of the IN signalto further increase, as shown between times T3 and T4. At time T4, thepass gate circuit 230 is activated by an active SAL2 signal to providethe voltage of the sense line DL to the input of the amplifier circuit210, as shown by the IN signal. As a result, the logic level of the OUTsignal is latched and the voltage of the sense line DL corresponds tothe data that was stored by the memory cell MC. Thus, the voltage of thesense line DL may be used to write back data to the activated memorycell MC for those embodiments of the disclosure where write back isnecessary.

FIG. 4 is a schematic diagram of a sense amplifier 400 according to anembodiment of the disclosure. The sense amplifier 400 may be used as asense amplifier 118 in the apparatus 110 of FIG. 1 in some embodimentsof the disclosure. The sense amplifier 400 may be coupled to a senseline DL that is used to provide a voltage corresponding to data storedby a memory cell MC. The memory cell MC may be accessed by activating anaccess line WL to cause a voltage stored by the memory cell MC to beprovided to the sense line DL. As previously described, the voltagestored by the memory cell MC corresponds to data, for example, a firstvoltage corresponds to a “1” bit of data and a second voltagecorresponds to a “0” bit a data. The change in voltage caused bycoupling the memory cell MC to the sense line DL is sensed and amplifiedby a sense amplifier, for example, the sense amplifier 400.

In some embodiments of the disclosure, for example, as shown in FIG. 4,the memory cell MC of FIG. 4 may be a volatile memory cell that includesa memory cell switch SW and a memory cell capacitor CCELL. As with thememory cell MC of FIG. 2, however, the scope of the disclosure is notintended to be limited to an particular type of memory cell and in otherembodiments of the disclosure the memory cell MC may be different thanthat shown in FIG. 4.

The sense amplifier 400 includes an amplifier circuit 410. The amplifiercircuit is configured to be coupled to a supply voltage and a referencevoltage. The amplifier circuit 410 receives a signal provided by thesense line DL and provides an output signal OUT having a voltagerepresenting output data. In some embodiments of the disclosure, theamplifier circuit 410 may be implemented as an inverter circuit, forexample, as shown in FIG. 4.

The sense amplifier 400 further includes a calibration circuit 425 thatis provided an input signal IN. The calibration circuit 425 includes apass gate circuit 427 and an inverter circuit 429. The IN signal isprovided to an input of the inverter circuit 429 that is coupled to acapacitor 428, which is itself coupled to a reference voltage (e.g.,reference voltage VSS). The pass gate circuit 427 couples the input andoutput of the inverter circuit 429 when activated by an activecalibration signal CALIB. The inverter circuit 429 is activated by anactive SALF signal (e.g., a high logic level SALF signal). The SALFsignal is the complement of the SAL signal. An inverter circuit 420included in the sense amplifier 400 is activated by an active latchsignal SAL. The inverter circuit 420 provides an output having a logiclevel complementary to the output signal of the amplifier circuit 410when activated by the SAL signal.

In contrast to the sense amplifier 200 of FIG. 2, the input of theamplifier circuit 410 of the sense amplifier 400 is not coupled to thesense line DL through a capacitor. The sense amplifier 400 may be usedwhen it is desirable for a capacitor to not be used to couple the senseline DL to the input of the amplifier circuit.

A precharge circuit 440 precharges the sense line DL when activated bythe precharge activation signal WRITE by setting a voltage of the senseline DL to the precharge voltage WRITEVAL in preparation for a senseoperation by the sense amplifier 400. The precharge circuit 440 may beimplemented as a pass gate circuit in some embodiments of thedisclosure, for example, as shown in FIG. 4. As previously described, insome embodiments of the disclosure, the precharge voltage is 0.6 volts,which may be one-half the supply voltage. Other voltage values may beused in other embodiments of the disclosure.

Operation of the sense amplifier 400 will be described with reference toFIGS. 4 and 5. FIG. 5 is a timing diagram showing various signals duringoperation of the sense amplifier 400 according to an embodiment of thedisclosure.

With reference to FIG. 5, prior to time T0, the memory cell MC isdeactivated by inactive access line WL, and the sense line DL isprecharged to a precharge voltage. The sense line DL is prechargedthrough the precharge circuit 440 which is activated by the active WRITEsignal to provide the WRITEVAL voltage to the sense line DL. Theprecharge voltage WRITEVAL is shown in FIG. 5 to be 0.6 volts in theembodiment of FIG. 5. The precharge voltage may be other voltages inother embodiments of the disclosure, however. Also prior to time T0, theinverter circuit 420 is deactivated by an inactive SAL signal. While thepass gate circuit 427 of the calibration circuit 425 is deactivated byan inactive CALIB signal, the inverter circuit 429 of the calibrationcircuit 425 is activated by an active SALF signal (i.e., the complementto the inactive SAL signal). As a result, the voltage of the IN signalapplied to the input of the inverter circuit 429 causes the invertercircuit 429 to provide a high logic level output signal. The high logiclevel output signal of the inverter circuit 429 is provided to theoutput of the amplifier circuit 410, as shown in FIG. 5 by a high logiclevel OUT signal. The input of the amplifier circuit 410 is provided theWRITEVAL voltage from the precharge sense line DL.

At time T0, the pass gate circuit 427 of the calibration circuit 425 isactivated by an active CALIB signal to couple together the input andoutput of the inverter circuit 429. The coupling of the input and outputof the inverter circuit 429 causes the voltages at the input and outputof the inverter circuit 429 to equalize to an equilibration voltagebetween the low logic level voltage and the high logic level voltage, asshown in FIG. 5 by the IN and OUT signals. In some embodiments of thedisclosure, the equilibration voltage is one-half of the supply voltage.However, it will be appreciated that the scope of the disclosure is notintended to be limited to an equilibration voltage of specificallyone-half of the supply voltage. The resulting voltage of the input andoutput of the inverter circuit 429 is provided to the output of theamplifier circuit 410. The coupling of the input and output of theinverter circuit 429 and providing the resulting voltage to the outputof the amplifier circuit 410 causes the output to be at a voltagecorresponding to an equilibrium point for the amplifier circuit 410. Aspreviously described, the equilibrium point may be the conditioncorresponding to the maximum gain of the amplifier circuit 410.Providing the equilibration voltage to the output may compensate forvariations of the amplifier circuit 410 from ideal amplifiercharacteristics. For example, deviation from ideal amplifiercharacteristics due to circuit mismatch, threshold voltage variations,voltage offsets, etc. may be corrected by forcing the output of theamplifier circuit 410 to the equilibration voltage.

At time T1, the precharge circuit 440 is deactivated by the inactiveWRITE signal to decouple the sense line DL from the WRITEVAL voltage.Following time T1, the pass gate circuit 427 is deactivated bydeactivation of the CALIB signal to decouple the input and output of theinverter circuit 429. Although with the pass gate circuit 427deactivated and the output and input of the inverter circuit 429decoupled, the voltage at the input is maintained by the capacitorcoupled between the input and the reference voltage, which in turncauses the voltage at the output of the inverter circuit 429 to bemaintained. Following deactivation of the pass gate circuit 427, theaccess line WL is activated to activate the memory cell MC for access.Upon activation of the memory cell MC at time T2, the voltage of thesense line DL is changed by the voltage corresponding to the data storedby the memory cell MC. At time T2, the memory cell MC accessed stores a“1” logic level, corresponding to a voltage greater than the prechargevoltage WRITEVAL. As a result, the activated memory cell MC causes thevoltage of the sense line DL to increase. The increase in the voltage ofthe sense line DL due to the activated memory cell MC is provided to theinput of the amplifier circuit 410. The increase in the voltage of theDL sense line causes the amplifier circuit 410 to provide acomplementary OUT signal having a decreasing voltage corresponding to alow logic level.

At time T3, the inverter circuit 420 is activated by an active SALsignal to provide a voltage to the sense line DL corresponding to a highlogic level, that is, the complement to the low logic level of the OUTsignal provided by the amplifier circuit 410. The high logic levelvoltage provided by the inverter circuit 420 to the sense line DL causesthe voltage of the sense line DL to increase, as shown between times T3and T4. The increasing voltage of the sense line DL is provided to theamplifier circuit 410, which further drives the OUT signal to the lowlogic level, as shown between times T3 and T4. Activation of theinverter circuit 420 at time T3 causes the data stored by the memorycell MC to be latched and the resulting voltage of the sense line DL maybe used to write back data to the activated memory cell MC for thoseembodiments of the disclosure where write back is necessary. At time T4,the inverter circuit 420 is deactivated by an inactive SAL signal, andadditionally, the inverter circuit 429 of the calibration circuit 425 isactivated by an active SALF signal (i.e., the complement to the inactiveSAL signal) to provide a high logic level output signal. The output ofthe amplifier circuit 410 is provided the high logic level output signalfrom the inverter circuit 429, as shown in FIG. 5 at time T4.

Operation of the sense amplifier 400 was previously described for amemory cell storing high logic level data. Operation of the senseamplifier 400 will also be described with reference to FIG. 5 for amemory cell storing low logic level data.

Prior to time T5, the memory cell MC is deactivated and the sense lineDL is precharged to the precharge voltage WRITEVAL. Also prior to timeT5, the inverter circuit 420 is deactivated by an inactive SAL signaland the inverter circuit 429 of the calibration circuit 425 is activatedby an active SALF signal (i.e., the complement to the inactive SALsignal). As a result, the voltage of the IN signal applied to the inputof the inverter circuit 429 through the capacitor 428 causes theinverter circuit 429 to provide a high logic level output signal. Thehigh logic level output signal of the inverter circuit 429 is providedto the output of the amplifier circuit 410, as shown in FIG. 5 by a highlogic level OUT signal. The input of the amplifier circuit 410 isprovided the WRITEVAL voltage from the precharged sense line DL.

At time T5, the pass gate circuit 427 of the calibration circuit 425 isactivated by an active CALIB signal and the voltages at the input andoutput of the inverter circuit 429 equalize to the equilibration voltagebetween the low logic level voltage at the input and the high logiclevel voltage at the output. The resulting voltage of the input andoutput of the inverter circuit 429 is provided to the output of theamplifier circuit 410. At time T6, the precharge circuit 440 isdeactivated by the inactive WRITE signal to decouple the sense line DLfrom the WRITEVAL voltage, and the pass gate circuit 427 is deactivatedby the deactivation of the CALIB signal to decouple the input and outputof the inverter circuit 429. While the pass gate circuit 427 isdeactivated, the voltage at the input of the inverter circuit 429 ismaintained by the capacitor coupled between the input and the referencevoltage, and the voltage at the output of the inverter circuit 429 ismaintained by the input voltage. Following the deactivation of the passgate circuit 427, the access line WL is activated to activate the memorycell MC for access. Upon activation of the memory cell MC at time T7,the voltage of the sense line DL is changed by the voltage correspondingto the data stored by the memory cell MC. At time T7, the memory cell MCaccessed stores a “0” logic level, corresponding to a voltage less thanthe precharge voltage WRITEVAL, which causes the voltage of the senseline DL to decrease. The decrease in the voltage of the sense line DL isprovided to the input of the amplifier circuit 410. The decrease in thevoltage of the DL sense line causes the amplifier circuit 410 to providea complementary OUT signal having an increasing voltage corresponding toa high logic level.

At time T8, the inverter circuit 420 is activated by an active SALsignal to provide a voltage to the sense line DL corresponding to a lowlogic level, that is, the complement to the high logic level of the OUTsignal provided b the amplifier circuit 410. The low logic level voltageprovided by the inverter circuit 420 to the sense line DL causes thevoltage of the sense line DL to decrease, as shown at time T8. Thedecreasing voltage of the sense line DL is provided to the amplifiercircuit 410, which further drives the OUT signal to the high logiclevel, as shown at time T8. Activation of the it circuit 420 at time T8causes the data stored by the memory cell MC to be latched and theresulting voltage of the sense line DL may be used to write back data tothe activated memory cell MC for those embodiments of the disclosurewhere write back is necessary.

FIG. 6 is a schematic diagram of a sense amplifier 600 according to anembodiment of the disclosure. The sense amplifier 600 includes adifferential amplifier 610 that receives a first input signal PLUS at afirst input arid further receives a second input signal MINUS at asecond input. In some embodiments, the first input is provided a readreference voltage and the second input is coupled to a sense line DL.When activated by an active enable signal EN, the differential amplifier610 provides an output signal OUTDIFF at an output that has a voltagebased on the difference between the voltages at the first and secondinput signals. Data of a memory cell MC may be sensed and amplified bycomparing the read reference voltage provided to the first input to thevoltage of the sense line coupled to the second input and to which anactivated memory cell is coupled. The differential amplifier 610includes transistors 612 and 614 coupled as a current mirror circuit,and further includes an input transistor 616 that receives the PLUSsignal and an input transistor 618 that receives the MINUS signal. Thesense amplifier 600 further includes a buffer circuit 620. The buffercircuit 620 receives the OUTDIFF signal from the differential amplifier610, and when activated by an active EN signal, provides an outputsignal SAOUT that is the complement of the OUTDIFF signal. The buffercircuit 620 includes an inverter circuit that may be enabled by anactive EN signal.

Calibration circuits 630 and 640 included in the sense amplifier 600 arecoupled to the output of the differential amplifier 610 and the outputof the buffer circuit 620, respectively. The calibration circuit 630includes a pass gate circuit 632 and an inverter circuit 634. Thecalibration circuit 640 likewise includes a pass gate circuit 642 and aninverter circuit 644. The inverter circuit 634 provides an output thatis the complement of the input when activated by an active EN signal.When deactivated by an inactive EN signal, the inverter circuit 634provides a high logic level voltage due to its input being coupled to areference voltage (e.g., ground) through a capacitor. The pass gatecircuit 632 couples together the output and input of the invertercircuit 634 when activated by an active calibration signal CALIB.Similarly, the inverter circuit 644 provides an output that is thecomplement of the input when activated by an active EN signal andprovides a high logic level voltage when deactivated by an inactive ENsignal. The pass gate circuit 642 couples together the output and inputof the inverter circuit 644 when activated by an active CALIB signal. Insome embodiments, the calibration circuit 640 is not included. In suchembodiments, the buffer circuit 620 may be operated without compensationprovided by the calibration circuit 640.

A pull-up circuit 650 may be included in the sense amplifier 600 in someembodiments of the disclosure. The pull-up circuit 650 may provide theoutput of the buffer circuit 620 a supply voltage (e.g., VCC voltage)when activated by an active ENF signal (i.e., the complement of the ENsignal). While the pull-up circuit 650 is not included in someembodiments of the disclosure, the pull-up circuit 650 may be includedto set the output of the buffer circuit 620 to a known voltage when thesense amplifier 600 deactivated (i.e., an inactive EN signal and anactive ENF signal).

Operation of the sense amplifier 600 will be described with reference toFIGS. 6 and 7. FIG. 7 is a timing diagram showing various signals duringoperation of the sense amplifier 600 according to an embodiment of thedisclosure.

As previously described, in some embodiments, the first input (e.g.,PLUS input) is provided a read reference voltage and the second input(e.g., MINUS input) is coupled to a sense DL. Data of a memory cell MCmay be sensed and amplified by activating a corresponding access line WLto couple the memory cell MC to the sense line DL. The coupling of thememory cell MC to the sense DL may cause a change in a voltage of thesense line DL. The resulting voltage of the sense line DL may becompared with the read reference voltage provided to the first input andthe voltage difference amplified by the sense amplifier 600. Withreference to FIG. 7, prior to time T0, the memory cell MC is deactivatedby an inactive access line WL and the sense line DL coupled to thesecond input of the differential amplifier 610 is precharged to aprecharge voltage. The sense line DL is precharged through a prechargecircuit which is activated by the WRITE signal to provide a prechargevoltage (e.g., the WRITEVAL voltage) to the sense line DL. The prechargevoltage WRITEVAL is shown in FIG. 7 to be 0.6 volts in the embodiment ofFIG. 7. The precharge voltage may be other voltages in other embodimentsof the disclosure, however. Also prior to time T0, the differentialamplifier 610, the buffer circuit 620, and the inverter circuits 634 and644 of the calibration circuits 630 and 640 are deactivated by aninactive EN signal. The first and second inputs of the differentialamplifier 610 are coupled together to have the same voltage, which isthe WRITEVAL recharge voltage. The pull-up circuit 650, however, isactivated by the inactive EN signal (i.e., active ENF signal) to providethe supply voltage (e.g., a VCC voltage) to the output of the buffercircuit, as shown in FIG. 7.

The pass gate circuits 632 and 642 of the calibration circuits 630 and640 are activated by an active CALIB signal to couple the input andoutput of the inverter circuit 634 and couple the input and output ofthe inverter 644. As previously discussed, the inverter circuits 634 and644 provide a high logic level output when deactivated by an inactive ENsignal. With the pass gate circuits 632 and 642 activated and theinverter circuits 634 and 644 deactivated, the voltage of the input andoutput are set to the supply voltage reduced by a voltage drop across apull up transistor of the inverter circuits. The resulting voltage ofthe input and output of the inverter circuit 634 is provided to theoutput of the differential an circuit 610. The resulting voltage of theinput and output of the inverter circuit 644 is provided to the outputof the buffer circuit 620. The output of the buffer circuit 620,however, is provided the supply voltage by the activated pull-up circuit650, which is activated by an inactive EN signal.

At time T0, the pull-up circuit 650 is deactivated, and the differentialamplifier 610, the buffer circuit 620, and the inverter circuits 634 and644 of the calibration circuits 630 and 640 are activated by an activeEN signal. With the inverter circuits 634 and 644 of the calibrationcircuits 630 and 640 activated, and the pass gate circuits 632 and 642still activated by the active CALIB the voltage provided at the outputsof the inverter circuits 634 and 644 equalize at a voltage between thelow logic level voltage and the high logic level voltage (e.g., one-halfthe voltage difference between VSS and VCC). The resulting voltage atthe output of the inverter circuit 634 is provided to the output of thedifferential amplifier 610 and the resulting voltage at the output ofthe inverter circuit 644 is provided to the output of the buffer circuit620.

Activating the calibration circuits 630 and 640 and providing theresulting voltage to the output of the amplifier circuit 610 causes theoutput to be at a voltage corresponding to an equilibrium point for theamplifier circuit 610 and for the buffer circuit 620. As previouslydescribed, the equilibrium point may be the condition corresponding tothe maximum gain of the amplifier circuit 610. Similarly, theequilibrium point may be the condition corresponding to the maximum gainof the amplifier circuit 610. Providing the equilibration voltage to theoutput of the amplifier circuit 610 and the buffer circuit 620 maycompensate for variations of the amplifier circuit 610 and the buffercircuit 620 from ideal circuit characteristics. For example, deviationfrom ideal circuit characteristics due to circuit mismatch, thresholdvoltage variations, voltage offsets, etc. may be corrected by forcingthe output of the amplifier circuit 610 and the butler circuit 620 tothe equilibration voltage. As previously discussed, in some embodiments,the calibration circuit 640 may not be included and the buffer circuit620 may be operated without being calibrated as previously discussed.

At time T1, the pass gate circuits 632 and 642 are deactivated by theCALIB signal becoming inactive to decouple the inputs and outputs of theinverter circuits 634 and 644. Additionally, the first and second inputsof the differential amplifier 610 are decoupled from one another so thatthe second input receives a voltage from the sense line DL and the firstinput receives the read reference voltage. The precharge circuit isdeactivated by the inactive WRITE signal to decouple the sense line DLfrom the WRITEVAL voltage and to allow the voltage of the sense line DLto be affected by a voltage corresponding to the data stored by a memorycell MC. Following the deactivation of the pass gate circuits 632 and642 and decoupling of the first and second inputs, the access line WL isactivated thereby activating the memory cell MC for access. Uponactivation of the memory cell MC, the voltage at the second input of thedifferential amplifier 610 is changed by the voltage corresponding tothe data stored by the memory cell MC. At time T1, the memory cell MCaccessed stores a “0” logic level, corresponding to a voltage less thanthe precharge voltage. As a result, the activated memory cell MC causesthe voltage at the second input of the differential amplifier 610 (i.e.,the MINUS signal) to decrease, as shown in FIG. 7. The decrease in thevoltage of the MINUS signal provided to the second input of thedifferential amplifier 610 causes the differential amplifier 610 toprovide a complementary OUTDIFF signal having an increasing voltage. Theincreasing voltage of the OUTDIFF signal causes the activated buffercircuit 620 to provide a complementary SAOUT signal corresponding to alow logic level voltage, as shown in FIG. 7 between times T1 and T2. Theresulting voltage provided by the activated buffer circuit 620 may beused to write back data to the activated memory cell MC for thoseembodiments of the disclosure where write back is necessary.

At time T2, the memory cell MC is deactivated by an inactive WL line andthe pass gate circuits 632 and 642 are activated by an active CALIBsignal. Also at time T2 the differential amplifier 610, the buffercircuit 620, and the inverter circuits 634 and 644 of the calibrationcircuits 630 and 640 are deactivated, and the pull-up circuit 650 isalso activated by an inactive EN signal. The precharge circuit is alsoactivated by an active WRITE signal to precharge the sense line DL tothe WRITEVAL precharge voltage, and the first and second inputs of thedifferential amplifier 610 are coupled together to have the samevoltage, which is the WRITEVAL precharge voltage of the sense line DL.

Operation of the sense amplifier 600 was previously described for amemory cell storing low logic level data. Operation of the senseamplifier 600 will also be described with reference to FIG. 7 for amemory cell MC storing high logic level data.

Prior to time T3, the sense amplifier 600 is in the same condition asprior to time T0 previously described. At time T3, the pull-up circuit650 is deactivated, and the differential amplifier 610, the buffercircuit 620, and the inverter circuits 634 and 644 of the calibrationcircuits 630 and 640 are activated by an active EN signal. With theinverter circuits 634 and 644 of the calibration circuits 630 and 640activated, and the pass gate circuits 632 and 642 still activated by theactive CALIB signal, the voltage provided at the outputs of the invertercircuits 634 and 644 equalize at a voltage between the low logic levelvoltage and the high logic level voltage (e.g., one-half the voltagedifference between VSS and VCC). The resulting voltage at the output ofthe inverter circuit 634 is provided to the output of the differentialamplifier 610 and the resulting voltage at the output of the invertercircuit 644 is provided to the output of the buffer circuit 620.

At time T4, the pass gate circuits 632 and 642 are deactivated by theCALIB signal becoming inactive to decouple the inputs and outputs of theinverter circuits 634 and 644. The precharge circuit is deactivated bythe inactive WRITE signal to decouple the sense line DL from theWRITEVAL voltage. Following the deactivation of the pass gate circuits632 and 642 and the precharge circuit at time T4, the access line WL isactivated thereby activating the memory cell MC for access. Uponactivation of the memory cell MC, the voltage at the second input of thedifferential amplifier 610 is changed by the voltage corresponding tothe data stored by the memory cell MC. At time T4, the memory cell MCaccessed stores a “1” logic level, corresponding to voltage greater thanthe WRITEVAL precharge voltage. As a result, the activated memory cellMC causes the voltage at the second input of the differential amplifier610 (i.e., the MINUS signal) to increase, as shown in FIG. 7 at time T4.The increase in the voltage of the MINUS signal provided to the secondinput of the differential amplifier 610 causes the differentialamplifier 610 to provide a complementary OUTDIFF signal having adecreasing voltage. The decreasing voltage of the OUTDIFF signal causesthe activated buffer circuit 620 to provide a complementary SAOUT signalcorresponding to a high logic level voltage, as shown in FIG. 7 betweentimes T4 and T5. The resulting voltage provided by the activated buffercircuit 620 may be used to write back data to the activated memory cellMC for those embodiments of the disclosure where write back isnecessary.

At time T5, the memory cell MC is deactivated by an inactive WL line andthe pass gate circuits 632 and 642 are activated by an active CALEBsignal. Also at time T5 the differential amplifier 610, the buffercircuit 620, and the inverter circuits 634 and 644 of the calibrationcircuits 630 and 640 are deactivated, and the pull-up circuit 650 isalso activated by an inactive EN signal. The precharge circuit is alsoactivated by an active WRITE signal to precharge the sense line DL tothe WRITEVAL precharge voltage, and the first and second inputs of thedifferential amplifier 610 are coupled together to have the samevoltage, which is the WRITEVAL precharge voltage of the sense line DL.As a result, following time T5, the sense amplifier 600 returns to thesame condition as prior to time T3 previously described.

FIG. 8 is a schematic diagram of a pass gate circuit 800 according to anembodiment of the disclosure. The pass gate 800 includes a firsttransistor 810 and a second transistor 820. The first transistor 810 isshown as a p-channel field effect transistor (pFET) and the secondtransistor 820 is shown as an n-channel field effect transistor (nFET)in FIG. 8. Sources and drains of the first and second transistors 810and 820 are coupled to common nodes. An input signal IN is provided to afirst common node 830 and an output signal is provided from a secondcommon node 840. A gate of the second transistor 820 is provided anactivation signal ACT and a gate of the first transistor 810 is providedthe complement of the ACT signal, which is provided by an invertercircuit 850. In operation, the pass gate circuit 800 provides the INsignal as the OUT signal when activated by an active ACT signal (e.g., ahigh logic level ACT signal).

In some embodiments of the disclosure, the pass gate circuit 800 may beused for various ones of the pass gate circuits previously described.For example, the pass gate circuit 800 may be used as the pass gatecircuit in the calibration circuit 225, the pass gate circuit 230, thepass gate circuit in the precharge circuit 240, the pass gate circuit427, the pass gate circuit in the precharge circuit 440, and the passgate circuits 632 and 642. The ACT signal may be provided by the CALIBsignal, SAL2 signal, or WRITE signal corresponding to the particular useof the pass gate circuit 800.

FIG. 9A is a schematic diagram of an inverter circuit 900 according toan embodiment of the disclosure. The inverter circuit 900 includes pFETs910 and 920, and further includes nFETs 930 and 940. The pFET 920 andthe NFET 930 are configured as an inverter and the pFET 910 and nFET 940are configured to enable the inverter by providing the reference voltageVSS to the nFET 930 and providing the supply voltage VCC to the pFET 920when activated by an active activation signal ACT and the complement ofthe ACT signal, which is provided by the inverter circuit 950. Gates ofthe pFET 920 and the nFET 930 are provided an input signal IN and anoutput signal OUT is provided from a common node 945 between the pFET920 and the nFET 930. In operation, the inverter circuit 900 provides anOUT signal that is the complement of the IN signal when activated by anactive ACT signal (e.g., logic high level).

In some embodiments of the disclosure, the inverter circuit 900 may beused for various ones of the inverter circuits previously described. Forexample, the inverter circuit 900 may be used as the inverter circuits220, 420, and 429. The ACT signal may be provided by the SAL signal andthe SALF signal corresponding to the particular use of the invertercircuit 900.

FIG. 9B is a schematic diagram of an inverter circuit 960 according toan embodiment of the disclosure. The inverter circuit 960 includes apFET 970, an nFET 980 and an nFET 990. The pFET 970 and the nFET 980 areconfigured as an inverter, and the nFET 990 is configured to enable theinverter by providing the reference voltage VSS to the nFET 980 whenactivate by an enable signal EN. Gates of the pFET 970 and the nFET 980are provided an input signal IN and an output signal OUT is providedfrom a common node 985 between the pFET 970 and the nFET 980. Inoperation, the inverter circuit 960 provides an OUT signal that is thecomplement of the IN signal when activated by an active EN signal (e.g.,logic high level).

In some embodiments of the disclosure, the inverter circuit 960 may beused for various ones of the inverter circuits previously described. Forexample, the inverter circuit 960 may be used as the inverter circuits620 and 634. The EN signal may be provided by the EN signalcorresponding to the particular use of the inverter circuit 960.

FIG. 10 is a block diagram of a memory 1000 including a sense amplifieraccording to an embodiment of the disclosure. The memory 1000 includes amemory array 1002 of memory cells, which may be, for example, volatilememory cells (e.g., DRAM memory cells, SRAM memory cells, etc.),non-volatile memory cells (e.g., ferroelectric memory cells, flashmemory cells, PCM cells, etc.), or some other types of memory cells. Thememory array 1002 may be implemented by the memory array 110 of FIG. 1,and include sense lines DL coupled to sense amplifiers according to anembodiment of the disclosure.

The memory 1000 includes a command decoder 1006 that receives memorycommands through a command bus 1008 and generates corresponding controlsignals within the memory 1000 to carry out various memory operations.The command decoder 1006 responds to memory commands applied to thecommand bus 1008 to perform various operations on the memory array 1002.For example, the command decoder 1006 is used to generate internalcontrol signals to read data from and write data to the memory array1002. Row and column address signals are applied to the memory 1000through an address bus 1020 and provided to an address latch 1010. Theaddress latch then outputs a separate column address and a separate rowaddress.

The row and column addresses are provided by the address latch 1010 to arow address decoder 1022 and a column address decoder 1028,respectively. The column address decoder 1028 selects bit linesextending through the memory array 1002 corresponding to respectivecolumn addresses. The row address decoder 1022 includes word linedrivers that activate respective rows of memory cells in the memoryarray 1002 corresponding to received row addresses. The selected dataline (e.g., a bit line or bit lines) corresponding to a received columnaddress are coupled to a read/write circuitry 1030 to provide read datato a data output buffer 1034 via an input-output data bus 1040. Writedata are applied to the memory array 1002 through a data input buffer1044 and the memory array read/write circuitry 1030.

From the foregoing it will be appreciated that, although specificembodiments the disclosure have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the disclosure. Accordingly, the scopedisclosure should not be limited any of the specific embodimentsdescribed herein.

What is claimed is:
 1. An apparatus comprising: an amplifier circuithaving an input and an output and configured to be coupled to a supplyvoltage and a reference voltage, when activated the amplifier circuitconfigured to provide an output signal at the output that iscomplementary to an input signal provided to the input; and acalibration circuit coupled to the output of the amplifier circuit, whenactivated by a calibration signal the calibration circuit configured toprovide a calibration voltage to the output of the amplifier circuit,wherein the calibration voltage is an equilibration voltage between thesupply voltage and the reference voltage provided to the amplifiercircuit.
 2. The apparatus of claim 1 wherein the amplifier circuitcomprises: an inverter circuit.
 3. The apparatus of claim 1, furthercomprising: a capacitor coupled between the input of the amplifiercircuit and a sense line.
 4. The apparatus of claim 3, furthercomprising: a pass gate circuit configured to couple the input of theamplifier circuit to the sense line when activated.
 5. The apparatus ofclaim 1 wherein the calibration circuit comprises: a pass gate circuitconfigured to couple the output of the amplifier circuit to the input ofthe amplifier circuit when activated by an active calibration signal. 6.The apparatus of claim 5, further comprising: a buffer circuit having aninput coupled to the output of the amplifier circuit and further havinga buffer output, the buffer circuit configured to provide a bufferoutput signal at the buffer output responsive to the output signal fromthe amplifier circuit, wherein the buffer output signal is thecomplement of the output signal from the amplifier circuit.
 7. Theapparatus of claim 1 wherein the calibration circuit comprises: aninverter circuit configured to be coupled to a supply voltage and areference voltage, the inverter circuit having an inverter input and aninverter output, wherein the inverter output is coupled to the output ofthe amplifier; a capacitor coupled to the input of the inverter circuit;and a pass gate circuit configured to couple the inverter output to theinverter input responsive to a calibration signal.
 8. The apparatus ofclaim 7 wherein the amplifier circuit comprises: a second invertercircuit.
 9. The apparatus of claim 8, further comprising: a second passgate circuit configured to provide a precharge voltage to an input ofthe second inverter circuit when activated by an active prechargesignal, wherein the calibration circuit is activated to provide thecalibration voltage to an output of the second inverter circuit duringactivation of the second pass gate circuit to provide the prechargevoltage to the input of the second inverter circuit.
 10. The apparatusof claim 7 wherein the amplifier circuit comprises: a differentialamplifier having a first input and a second input.
 11. The apparatus ofclaim 10 wherein the first input and the second input are configured tobe coupled together during activation of the calibration circuit toprovide the calibration voltage to an output of the differentialamplifier.
 12. An apparatus, comprising: an inverter circuit having aninverter input and an inverter output; a pass gate circuit configured tocouple the output to the input; and a capacitor coupled to the inverterinput.
 13. The apparatus of claim 12, further comprising: a sense linecoupled the capacitor, the sense line configured to provide a voltage tothe capacitor to be sensed by the inverter circuit.
 14. The apparatus ofclaim 12, further comprising: an amplifier circuit having an amplifierinput and an amplifier output, wherein the inverter output is coupled tothe amplifier output.
 15. The apparatus of claim 14, further comprising:a buffer circuit coupled to the amplifier output.
 16. The apparatus ofclaim 14 wherein the amplifier circuit comprises: a second invertercircuit.
 17. The apparatus of claim 14 wherein the amplifier circuitcomprises: a differential amplifier.
 18. An apparatus, comprising: adifferential amplifier having first and second inputs and an output, thedifferential amplifier configured to provide an output signal at theoutput responsive to first and second input signals provided to thefirst and second inputs, respectively, wherein the output signal havinga voltage based on a voltage difference between a first voltage of thefirst input signal and a second voltage of the second input signal; abuffer circuit having an input coupled to the output of the differentialamplifier and further having an output, the buffer circuit configured toprovide an output signal that is the complement of the output signalfrom the differential amplifier; a first calibration circuit coupled tothe output of the differential amplifier, the first calibration circuitconfigured to provide a first calibration voltage to the output of thedifferential amplifier prior to the differential amplifier providing theoutput signal responsive to the first and second input signals; and asecond calibration circuit coupled to the output of the buffer circuit,the second calibration circuit configured to provide a secondcalibration voltage to the output of the buffer circuit prior to thebuffer circuit providing the output signal that is the complement of theoutput signal from the differential amplifier, wherein the firstcalibration voltage provided by the first calibration circuit providesoffset cancellation for the amplifier circuit and the second calibrationvoltage provided by the second calibration circuit provides offsetcancellation for the buffer circuit.
 19. The apparatus of claim 18wherein the first calibration circuit comprises: an inverter circuithaving an inverter input and an inverter output; a pass gate circuitconfigured to couple the inverter output and the inverter input toprovide the first calibration voltage when activated by an activecalibration signal; and a capacitor coupled to the inverter input. 20.The apparatus of claim 19 wherein the inverter circuit is configured tobe provided a supply voltage and a reference voltage and wherein thefirst calibration voltage is an equilibration voltage between the supplyvoltage and the reference voltage.
 21. The apparatus of claim 19 whereinthe second calibration circuit is configured the same as the firstcalibration circuit.
 22. A method, comprising: coupling an equilibrationvoltage between a supply voltage and a reference voltage to an output ofan amplifier circuit; decoupling the equilibration voltage from theoutput of the amplifier circuit; applying an input voltage to an inputof the amplifier circuit; and providing an output voltage at the outputof the amplifier circuit that is the complement of the input voltage.23. The method of claim 22 wherein coupling the equilibration voltagebetween the supply voltage and the reference voltage to the output ofthe amplifier circuit comprising: coupling the output of the amplifiercircuit to the input of the amplifier circuit.
 24. The method of claim22 wherein coupling the equilibration voltage between the supply voltageand the reference voltage to the output of the amplifier circuitcomprising: coupling an output of an inverter circuit to an input of theinverter, wherein the inverter is configured to be coupled to the supplyvoltage and to the reference voltage.
 25. The method of claim 22 whereinthe amplifier circuit comprises an inverter circuit.
 26. The method ofclaim 22 wherein the amplifier circuit comprises a differentialamplifier.
 27. The method of claim 22, further comprising: activating amemory cell and providing a voltage corresponding to data stored in theactivated memory cell to a sense line, wherein the sense line is coupledto the input of the amplifier circuit.
 28. The method of claim 27,further comprising: buffering the output voltage of the output of theamplifier circuit with an inverter circuit; and writing back the datastored in the activated memory cell using the output voltage of theinverter circuit.